Sexual conflict can potentially lead to sexually antagonistic coevolution (SAC), commonly described as arms races between male and female reproductive traits that arise as each sex attempts to maximize its fitness at a cost to the other sex. Recently, many studies have attributed the rapid evolution of male reproductive genes in a diversity of taxa to reproductive conflict. However, to determine sexual conflict genes, the influences of other reproductive processes must be taken into account. This task has traditionally been difficult because reproductive trait evolution has generally been examined only in gonochoristic species that contain both males and females without comparison with closely-related non-gonochoristic species. Furthermore, though SAC requires participation from male and female reproductive components, efforts discerning female contribution have lagged far behind, with only a few female receptors to male-transferred proteins identified. Here, we propose to exploit the genomic and molecular biology tools available in four species of the worm genus Caenorhabditis that differ in mating systems to test the effects of SAC on gene evolution. The data generated here will form the basis for future functional studies. These comprehensive studies may represent one of the first to address the influences of SAC on gene evolution and function in multiple species on a genome-wide scale. Nematodes are highly speciose and are distributed worldwide, impacting human populations not only through their infection of agricultural products but also through direct infection of human beings. The WHO estimated that at least two billion people worldwide suffer from nematode infections, with approximately one billion suffering from intestinal nematode infections alone. As some of the most well studied species in Nematoda, the species of Caenorhabditis represent valuable models that may provide insight on this medically important phylum. The research training plan that we have described in this submission will greatly enhance the applicant<s conceptual understanding of an important force in the evolution of diversity and natural variation. Additionally, the applicant will develop many practical molecular biology skills in a model system that is new to her. This project is highly novel because it takes advantage of an organism (C. elegans) that was primarily used as a developmental genetic model, and along with its sibling species, to address questions related to sexual conflict and the genetic and genomic changes that accompany mating system evolution in animals. Finally, the training and mentorship provided by Drs. Rockman and Purugganan will aptly prepare the applicant for a successful academic and research career.